Distal Upper Extremity Block

Published on 06/02/2015 by admin

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Last modified 06/02/2015

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8 Distal Upper Extremity Block

Ulnar, Median, and Radial Block at the Elbow

Perspective

In general, distal upper extremity blocks—those at the elbow or wrist—are not frequently required if facility with more proximal blocks is gained. These more distal peripheral blocks are perceived to be associated with a slightly higher likelihood of nerve injury, perhaps because many of the peripheral branches are anatomically located in sites where the nerve is contained within bony and ligamentous surroundings. Although it is not difficult to localize the nerves at these peripheral sites, especially with ultrasonographic guidance, the “entrapment” of these nerves makes more proximal blocks, such as the axillary block, my preferred approach. Further, because a significant portion of hand and forearm surgery is carried out using an upper arm tourniquet, use of more distal blocks mandates significantly heavier sedation so that the patient can tolerate tourniquet inflation pressures.

Patient Selection

Few patients should require distal upper extremity block; an exception might be those needing supplementation after brachial plexus block. In any event, comprehensive anesthesia care should be possible without frequent use of these blocks.

Pharmacologic Choice

These peripheral blocks are usually considered for superficial surgery; thus, lower concentrations of local anesthetic are appropriate because motor blockade should not be an issue. Therefore, 0.75% to 1% mepivacaine or lidocaine, or 0.25% bupivacaine, or 0.2% ropivacaine should be sufficient.

Of the three major nerves at the elbow—radial, median, and ulnar—the ulnar is most predictable in location. As illustrated in Figure 8-1, the ulnar nerve is located in the ulnar groove, which is a bony fascial canal between the medial epicondyle of the humerus and the olecranon process. This area is extremely well protected by fibrous tissue and, although it may seem at first like an easy site to carry out block, the nerve is well protected (and potentially vulnerable) in the ulnar groove. The median nerve at the elbow lies medial to the brachial artery, which lies just medial to the biceps muscle. Conversely, the radial nerve has a somewhat variable course; it pierces the lateral intramuscular septum on its way to the forearm, and lies between the brachialis muscle and the brachioradialis muscle in the distal aspect of the upper arm. It is more effectively blocked in the axilla than at the elbow.

Figure 8-1. Elbow nerve blocks: functional anatomy.

Position

All three of these nerves are blocked with the patient in the supine position and the arm supinated and abducted at the shoulder at a 90-degree angle. In addition, when the ulnar nerve block is performed, the forearm is flexed on the upper arm to more easily identify the ulnar groove (as illustrated in Fig. 8-3).

Needle Puncture: Median Nerve Block

A line should be drawn between the medial and lateral epicondyles of the humerus (at the level of the “pane of glass” shown in Fig. 8-1). Immediately medial to the brachial artery, the needle is inserted in the plane of the pane of glass, and a paresthesia is sought or a nerve stimulator or ultrasonographic guidance is used to direct the needle (Fig. 8-2). After the needle is positioned, 3 to 5 mL of solution is injected medial to the brachial artery.